Improvements to msbuild scripts in NuGet package:

Support for installing the resulting TapPackage after it is created (on by default)

Controlled by a property in the project file like this:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <InstallCreatedOpenTapPackage>true</InstallCreatedOpenTapPackage>
    ...

Support for adding assembly references to payload assemblies in included AdditionalOpenTapPackages

Whether to add references to dlls in a specific OpenTAP package is controlled by the new Reference attribute like this:

<Project Sdk="Microsoft.NET.Sdk">
  <ItemGroup>
    <AdditionalOpenTapPackage Include="DMM API" Reference="true" /> 
    ...

Or by using new OpenTapPackageReference items (this should probably be our recommended/documented approach)

<Project Sdk="Microsoft.NET.Sdk">
  <ItemGroup>
    <OpenTapPackageReference Include="DMM API"/> 
    ...

Closes #57 (closed)